Krsna enters within the universe, but at the same time, millions of universes are within His mouth. This is the explanation of "the greater than the greatest and the smaller than the smallest." Of course, mother Yasoda, although she saw, she could not believe it because mother Yasoda never thought of that Krsna is the Supreme Personality of Godhead. She always thought that "He is my teeny child." That's all. "I have to take care of Him." This is called paternal feelings. Vatsalya-rasa.
Lecture on Bhagavad-gita 2.25, Hyderabad, 29 November, 1972